Building string programatically and dealing with trailing or leading boolean operators

Question

I am using Lucene in an application. As such I have a form that lets users build a query by selecting what they want to search from dropdowns. Once a user submits, I build the query and it comes down to something like this:

var formedQuery= string.Empty;
foreach(var field in fields)
{
    if (field.name != 'condition so you never know which field from fields will be 1st')
        formedQuery += " AND" + field.name + ":" field.value;
}

Now the problem with this is that the statement will begin with ' AND'

Now I usually finish with:

formedQuery = formedQuery.Substring(4) //Trim the first 4 characters

Would fellow programmers usually prefer to do:

var formedQuery= string.Empty;
var i = false;
foreach(var field in fields)
{
    if (false && 
        field.name != 'condition so you never know which field from fields will be 1st')
    {
        formedQuery += " AND" + field.name + ":" field.value;
        i = true;
    }
    else
        formedQuery += " " + field.name + ":" field.value;
}

Is there another technique people like to use for this sort of thing I am not thinking of? I prefer the former.

Answer 1

I have always used the former. Mostly because it looks cleaner to me.

---

Another approach:

query = first_field_name

for every other field besides first:
    query = " AND " + field_name

Answer 2

There are two other solutions I use, depending a little on the language. The first is similar to your second one, but just changes the "first-field" check.

var formedQuery = string.Empty;
var and = string.Empty;
foreach(var field in fields)
{
    if (field.name != 'condition so you never know which field from fields will be 1st')
    {
        formedQuery += and + field.name + ":" field.value;
        and = " AND";
    }
}

But the solution I usually use involves an ordered list. Assuming I can extend your example code in any way that looks sensible:

var formedQuery = list.Empty;
foreach(var field in fields)
{
    if (field.name != 'condition so you never know which field from fields will be 1st')
    {
        formedQuery.push(field.name + ":" field.value);
    }
}
formedQuery = formedQuery.join(" AND ");

This also has the advantage of not making lots of unnecessary string copies as your assemble the string (in some languages, this is expensive).